A fat or oil is essential for a human body as nutrients and source of energy supply (the primary function), and moreover, are important for providing so-called sensory function (the secondary function), which satisfies palatability of foods, for example, taste or aroma. In addition, a fat or oil containing diacylglycerols at a high concentration is known to show physiological effects (the third function) such as body fat-burning effect.
An untreated fat or oil obtained by squeezing seeds, germs, pulp, and the like of plants contains, for example, fatty acids, monoacylglycerols, and odor components. Further, when the untreated fat or oil is processed, trace components are generated as by-products through a heating step such as a transesterification reaction, an esterification reaction, or a hydrogenation treatment, resulting in the deterioration of the taste and flavor of the resultant fat or oil. It is necessary to improve taste and flavor by removing these by-products in order to use the fat or oil as edible oils. Thus, a process of so-called deodorization, in which the fat or oil is brought into contact with water vapor under reduced pressure at high temperature, is generally performed (Patent Document 1).
Further, for a diacylglycerol-rich fat or oil, a method involving adding an organic acid to the fat or oil rich in diacylglycerols and then carrying out a decoloration treatment with a porous adsorbent, followed by deodorization treatment, so as to provide good taste and flavor (Patent Document 2), or a method involving carrying out an esterification reaction between glycerin and each of fatty acids obtained by hydrolyzing a raw material fat or oil by an enzymatic decomposition method and then carrying out a deodorization treatment so that the deodorization time and the deodorization temperature can be each controlled in a given range (Patent Document 3).